ts associated with soluble, lumenal proteins. The KK cluster did not contain any significant GO term enrichments. Conservation of amino acid sequences across species infers that these sequences are either essential for viability and/or essential for interaction with other proteins. We then used the Basic Local Alignment Search Tool to determine if the diarginine motif identified in the bioinformatic screen in the first mutant localized predominantly in the light fractions The di-arginine motif -a general ER AZD-2281 site retention motif In order to 24290880 determine whether the di-arginine motif regulates a diverse set of proteins in the cell, we randomly selected two further membrane proteins identified in the bioinformatic screen as containing a di-arginine motif in the first Discussion PLN is recycled via COP I mediated retrograde transport Previously, we have shown that the RSYQY amino acid sequence at the C-terminus of SLN is vital in its ER/SR localisation. The lack of this luminal sequence in PLN led us to pursue other mechanisms for PLN targeting to the ER/SR. In this study, we have shown that PLN retention in the ER is dependent on its RJuly RR Motif and PLN Targeting July RR Motif and PLN Targeting lipid chain-anchored membrane protein; and type the cell surface. These studies highlight the importance and versatility of the di-arginine motif in ER retention and provide a short amino acid sequence that is unrestricted by its positioning to the very C-terminal end of a protein, as is necessary with the dilysine motif. PLN expression has been observed outside of the ER, suggesting that it is not exclusively contained within the ER and indicating a requirement for further cellular trafficking mechanisms. In this study, we have established a possible mechanism for the trafficking of PLN. Retrograde transport from the golgi to the endoplasmic reticulum has been well studied and is clearly mediated by COP I coated vesicles. The minimal machinery necessary to form these retrograde transport vesicles has been shown to be only two proteins; coatomer protein and ARF Correct localization of PLN requires the intact di-arginine motif We then investigated further the involvement of the di-arginine motif at the N-terminus of PLN. 10875251 Our recent finding of a human deletion at Arg whereas PLN RD Cellular Component for RR motif nuclear membrane cytoplasmic membrane-bounded vesicle trans-Golgi network membrane-bounded vesicle cytoplasmic vesicle part Cellular Component for XDEL motif endoplasmic reticulum lumen membrane-enclosed lumen organelle lumen ER-Golgi intermediate compartment melanosome Count Ref. Count Raw p-value FDR p-value Cellular component enrichment of the RR and XDEL motif. GO-term cellular component analysis was carried out using ProteinCenter software suite on proteins identified 
in the bioinformatic screen as containing the di-arginine motif in the first July RR Motif and PLN Targeting specifically interact with COP I vesicles. Further evidence of the di-arginine motif binding to coatomer protein was provided more recently by key mutations made to the a and b subunit of COP I, which although led to the formation of the coatomer complex had lost its ability to bind to the di-lysine motif. In summary, we propose that PLN is retrieved from the golgi apparatus through the COP I retrograde pathway, and that COP I binds to the di-arginine motif in the cytoplasmic domain of PLN. A greater understanding of PLN protein synthesis and proper targeting in the cell